The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Treatment fluids used for treating subterranean formations in oil and/or gas wells are typically prepared at a surface location and pumped downhole through the well into the formation. Examples of treatments for subterranean formations are hydraulic fracturing, matrix acidizing, wellbore consolidation, gravel pack treatments, frac and pac treatments, well abandonment treatments, cementing treatments, wellbore clean-out operations, water control treatments, wellbore consolidation or wellbore strengthening treatments, and the like. One particular example of such a treatment is hydraulic fracturing. In one mode of operation, hydraulic fracturing is a process for stimulating oil and gas wells by pumping a hydraulic fracturing fluid formed as a viscosified slurry containing sand or proppant at high pressure into producing rock layers so that the formation is fractured or cracked. Once the rock is cracked, the resulting fracture is propped open by the proppant or sand carried by the slurry after the pressure is reduced. This propped fracture serves as a highly conductive path for the oil or gas, and therefore increases the effective producing well-bore radius. Fluid viscosity is vital for effective proppant placement during fracturing operations. Polysaccharides such as guar and guar derivatives have historically served as the most common viscosity enhancers. These polymers are often crosslinked using borates or metallic crosslinkers such as zirconium and titanium to generate even higher viscosity. For each fluid formulation, viscosity is predicted prior to pumping by tests performed during the fluid development phase. These results are typically reproduced with matching conditions (same lots of chemicals, same mix-water, same breaker concentrations and same well bottom-hole static temperature) prior to the treatment and adjustments are made when needed. Qualitative pre job quality assurance/quality control (QA/QC) is performed on location before beginning the pumping operation to ensure the fluid performs as required.
A major challenge in hydraulic fracturing operations and other treatments is how to ensure that the fluid that is being pumped matches the performance it was designed for. A limited number of samples of the fluid may be manually taken at significant events to ensure they match the fluid design, but this is only done periodically or sparsely. Additionally, treatment and/or fluid variables may have changed between the time the fluid is formed and pumped and the time the fluid sample is taken so that the properties of the actual treatment fluid no longer matches exactly those of the designed treatment fluid.
As an example, mix water used in forming the treatment fluid may contain an amount of iron. Iron can have a significant impact on the properties of the treatment fluid. The iron concentration of the water may therefore be measured prior to forming the treatment fluid to determine how much iron control agent must be added to the fluid. In certain cases, the iron concentration of the water may be measured hours or even days before the treatment fluid is formed. Preparation and design of the treatment fluid may be made based upon this measured iron concentration. When the treatment fluid is pumped, however, the iron concentration may have changed due to additional iron from tanks, pipes, etc. leaching into the water. Thus, the amount of iron control agent additive designed for the treatment may no longer be sufficient. Additionally, because the treatment is conducted as a continuous process with fluids being combined and mixed in a continuous flow as the treatment is carried out, the amount of iron in the water may change over time for various reasons. The properties of the iron control agent added to the treatment fluid may also change over time if a different lot is used during the treatment than what was used in the initial design. As can be seen, the treatment fluid properties of the initial design may no longer match the properties as they exist because of these changes.
Other variables that can have a considerable impact on the fluid performance and that can vary from frac tank to frac tank, or in time are enzyme concentration, bacteria count, active biocide concentration, water hardness (as Ca2+ or Mg2+ concentration), bicarbonate or carbonate concentration, pH, or mix water temperature.
In most cases, once the treatment has begun, there is very little monitoring of the fluid properties of the various treatment fluid components or the treatment fluid itself or adjusting the composition of the treatment fluid once the treatment has begun. If any are made, these are only sparse or periodic measurements. Typically, feedback regarding the treatment fluid properties is obtained through fluid pressure responses that are measured during the treatment. These measurements may have little to do with the properties of the treatment fluid and may have more to do with the response of the formation and properties of the well or completion. Thus, the treatment fluid formulation may be changed in response to a formation event, when it should have remained unaltered. Conversely, a friction change attributable to a fluid composition change could be mistakenly attributed to formation events and as a response a treatment may be shut down early, while a small formulation adjustment would have been the appropriate response. Therefore it is difficult to tell what has caused the change and whether it is a result of a property of the fluid or some other factor, without some appropriate monitoring or prediction of fluid properties.
Accordingly, a need exists for providing a method of performing a treatment and monitoring and controlling a treatment fluid wherein properties of the treatment fluid and its components can be monitored and taken into account to provide a more effective treatment fluid and treatment.